1. Field of the Invention
This invention relates to a liquid crystal mask type laser marking system for transferring pattern information onto an object to be worked.
2. Description of the Prior Art
Electric parts such as semiconductor devices or resistors are surrounded by insulating layers consisting of synthetic resin coating. Affixed to such an insulating layer is a pattern information in the form of a manufacturer's label, a production number, etc. Such pattern information has to be varied depending on the type of the electric part, manufacturing date, etc. Recently, a liquid crystal mask type laser marking system in which a pattern information can be changed from the outside has been getting attention. Examples of such marking system are disclosed in Japanese Patent Unexamined Publication No. 64-11088 (which corresponds to U.S. Pat. No. 4,818,835) and No. 2-165880.
A liquid crystal mask type laser marking device is designed to apply a laser beam to a liquid-crystal mask consisting of liquid crystal elements having a pattern information controllable from the outside. The laser beam passes through the liquid crystal mask to reach an object to be worked and partly evaporates the object with heat, thereby impressing the pattern information on the object.
In some electronic parts, such as printed boards or liquid crystal cells, an electric circuit is formed on a board by applying a photoresist to the surface of the board, exposing the photoresist to ultraviolet rays to effect development, and performing etching thereon. In the production of such electronic parts, the prior art laser marking techniques cannot be adopted for the following reasons:
1) The wavelength to which the photoresist is sensitive does not coincide with the wavelength of the infrared laser beam or the visible laser beam emitted from a laser oscillator. That is, the photoresist is not sensitive to the infrared or the visible laser beam.
2) If a laser beam having a wavelength to which the photoresist is sensitive, for example, a laser beam in the ultraviolet region, is irradiated to the liquid crystal mask, the liquid crystal molecules in the mask will decompose.